rdmd -cov generates bad file names with absolute directories or .. directories in -I flag

[timotheecour]

> It's not an RDMD issue, it's Druntime. Specifically the baseName
> function in src/rt/cover.d. This can easily be fixed.

Should I file a BUG/enhancement request?

> The problem is Druntime can't have dependencies to Phobos.

Sure, I meant reusing same functionality (rewritten in C++) so 
there's no dependency.


> This could be an enhancement. Or we could make cov generation 
> follow the -od switch.

No overloads, please: for example with rdmd, the output will be 
in a temp directory that the user shouldn't know about. An 
explicit switch would be needed, and the user can use same dir as 
for -od if he wishes to.